(1) Field of the Invention
This invention relates to the field of torque wrenches. More particularly, this invention relates to the field of manually operated torque wrenches in which the potential for drive back or kick back through the wrench poses a hazard to the operator of the wrench.
(2) Description of the Prior Art
Torque wrenches are well known in the art in which spur or planetary gears are used to transmit and multiply an input force to the wrench to the output of the wrench for purposes of applying torque to a nut or bolt or other fastening element. As is well known in the art, when a torque wrench of this type is used to apply a desired torque to tighten a nut or bolt, an equal and opposite reaction is created on the wrench which, unless restrained, will drive back through the wrench and pose a serious kick back hazard to the operator. Unless this reaction force is restrained, as soon as the operator lets go of the input handle, the input handle will be driven violently in the opposite direction (i.e., opposite from the direction in which it was being moved to apply torque), thereby posing a serious kick back hazard. In the past, the traditional approach to this problem has been to use a ratchet mechanism between input handle of the wrench and the gear train to prevent kick back. The ratchet mechanism permits motion of the input handle in one direction but restrains the handle against movement in the reverse direction. In the prior art approach, the entire reaction force generated in the wrench is imposed on the ratchet mechanism. In order to release the wrench from the nut or bolt, the operator must reapply the full torque load to the input or operating handle of the wrench to disengage the ratchet mechanism. While holding the wrench operating handle and resisting the full reaction load of the wrench, the operator must then release the ratchet mechanism to permit reverse rotation of the input handle, and the operator must then resist the full reaction load of the wrench while gradually permitting the handle to rotate in the reverse direction until the reaction load is dissipated. This unloading sequence requires the operator to resist the reaction load with just one hand while releasing the ratchet. Also, depending on the relative position of the operator with respect to the handle as the handle is rotated to relax the reaction load, it can become extremely difficult for the operator to maintain his grip on the handle and resist the reaction load. Furthermore, there is the danger at any time that, if the operator should let go of the handle for any reason, the entire unrelaxed reaction load will be immediately released resulting in violent kick back of the input handle which poses a serious hazard to the operator. Many serious injuries, including broken arms and operators being thrown from elevated positions, have been experienced because of the hazards presented by wrenches of this type.